Roll-up window shade with reduced-friction drive

ABSTRACT

Two drive gears are provided as an extension of the guide rails for driving a roll-up window shade for a motor vehicle. The drive gears are coupled to the winding shaft in a rotationally elastic manner. The driving is carried out via a geared motor, which acts either on the gears or on the winding shaft. The positioning of the drive gears as an extension of the guide rails avoids the guide tubes used in prior art arrangements. Thus, the friction losses found in the prior art, which consume up to 80% of the drive force, are avoided. Furthermore, manufacturing is simplified because the connection tubes having a complicated shape are not needed.

FIELD OF THE INVENTION

This invention relates to roll-up window shades for motor vehicles.

BACKGROUND OF THE INVENTION

Electrically driven rear window roll-up shades are known from the priorart. These prior art roll-up window shades have a winding shaft that ispivotably supported below the rear shelf and on which one edge of theshade is affixed. The other edge of the shade is connected to a tensionrod that is guided at its end by guide rails. The guide rails arearranged next to the lateral edges of the rear window and extend fromthe rear shelf or below it to the vicinity of the upper edge of thewindow. In order to pretension the shade, there is generally a springmotor in the winding shaft or next to it. This motor biases the windingshaft in the shade wind-up direction.

The unwinding or unfolding of the shade is carried out with the aid oflinear push elements that run in a buckle resistant manner in the grooveor slot chamber of the guide rails. A common gear motor is provided nextto the winding shaft approximately at the level of its center. Guidetubes are provided in order to connect the gear motor to the lower endsof the guide rails. The guide tubes end at the gear housing of thegeared motor. With the aid of these guide tubes, the push elements areconducted in a buckle-proof manner between the drive motor and the guiderails, so that they can carry out the pushing function.

Since the motor sits relatively close to the winding shaft because ofspace considerations, the guide tubes run more or less parallel to thewinding shaft in the vicinity of the geared motor and must be deflectedin the guide rails in a direction perpendicular to the winding shaft. Inturn, for space considerations, the radius of curvature of the guidetubes next to the point where they lead into the guide rails isrelatively very narrow.

Actual practice shows that with such shades, the push elements in theguide tubes consume the majority of the drive force produced by themotor. Only a comparatively small fraction of the drive force isactually needed to extend the shade.

The guide tubes generally have a relatively complicated,three-dimensional shape. As a result, their production and theiradaptation to motor vehicle conditions are difficult.

In addition, the push elements must also be protected in the sectionthat lies behind the motor relative to the line of sight. The length ofthis part of the push element, which projects above the motor, dependson the distance the shade extends. The push element projects least whenthe shade is extended, whereas the projection is greatest when the shadeis completely retracted. Since the travel is usually greater than halfthe width of the winding shaft, the storage tube taking up the excesspart must also be adapted in a complicated three-dimensional manner tothe available space in the motor vehicle. Thus, not only is themanufacturing of the roll-up window shade cumbersome, it also isdifficult to install in a motor vehicle.

The problems with known designs have been described in the context of arear window roll-up shade. Similar problems are found with roll-upwindow shades for sunroofs, which are driven in a comparable manner. Thehigh friction losses of the push elements in the guide and storage tubesalso create complications with regard to the design and dimensioning ofan electric-based pinch protection system, which is based on themeasurement of the motor current. Depending on the magnitude of thefriction losses, more or less force may be available at the giveninterruption current to catch or pinch body parts.

OBJECTS AND SUMMARY OF THE INVENTION

In view of the foregoing, a general object of the present invention isto provide a roll-up window shade for motor vehicles having a drive withlower friction losses.

The roll-up window shade of the invention includes a rotatably supportedwinding shaft. In the usual manner, one edge of the shade is affixed tothis winding shaft. The other edge of the shade is connected to atension rod, the ends of which run in guide rails. The guide railsextend on both sides of the extended shade and define the path which thetension rod travels between the retracted and extended positions of theshade.

The drive of the tension rod operates with the aid of two push elements.Each of the push elements is conducted by a corresponding guide rail.The ends of the two push elements act on the tension rod, so as to beable to move the tension rod away from the winding shaft.

Each push element is provided with its own drive gear. The drive gearcan be provided adjacent the foot end of the guide rail—i.e., in thevicinity of the winding shaft. Thus, a substantial piece of guide tubebetween the foot end of the guide rail and the drive gear can beomitted. The push element exiting from the individual guide rail can runsubstantially directly into a gear housing that is arranged adjacent tothe foot end of the guide rail. In this way, it is possible to reducethe cost of the connection tube.

Reducing the cost of the connection tube enables the drive force to besaved in two ways. First, the drive force which is required to move thecorresponding length of push element through a perhaps evenstraight-running guide tube can be omitted. Second, the friction forceis minimized because the connection tube does not have a curved shape,which caused the push element to encounter increased friction in theconnection tube. As a result, the drive force supplied by the motor isessentially entirely available for moving the shade. The friction forceproduced by the push elements in the guide rails is comparatively smallbecause the guide rails run almost straight.

An electrical drive motor is provided for driving the shade. The drivemotor simultaneously produces the force which is needed to wind up theshade during the retraction on the winding shaft and to move back thepush elements.

Additionally, a compensation mechanism is provided to compensate for thelength difference between the advance movement of the shade and the pushelement. The push element runs over a drive gear, whose diameter isconstant. Thus, for each turn of the drive gear, the same length of thepush element is always moved. The situation is different with the shade.The shade forms a spiral-shaped roll on the winding shaft. When theshade is unwound, the effective diameter of the roll, and thus thequantity of shade that is drawn from the winding shaft per turn,changes. The length difference is not excessively large but must becontrolled. This is where the compensation mechanism is used. Thecompensation mechanism produces the cloth tension on the shade.

Since a three-dimensional deflection of the push element does not occurwith the present invention, a push element that has a gear-tooth systemonly on one side can be used. Alternatively, a push element that has agear-tooth system all around can be used. The all-around gear-toothsystem enables positioning of the push element in the guide rail via akind of helical movement. Due to this helical movement, the push elementis “turned past,” so to speak, the fixed drive gear.

Depending on the vehicle body conditions, the push elements can eitherrun freely in the vehicle body or can run in storage tubes that are madeof a flexible material. The storage tubes can be placed anywhere in theautomobile body and do not have to be pre-shaped by the manufacturer ofthe roll-up window shade.

Very simple drive conditions can be produced if the drive motor iscoupled via gears directly to the winding shaft. With such anarrangement, either the drive gears are coupled in an elasticallyrotating manner with the winding shaft, or they sit on a connectionshaft that is conducted through or runs over the winding shaft. Use of aseparate connection shaft also allows the gears to fixed on theconnection shaft without rotational play and the connection shaft to becoupled to the winding shaft in a rotationally elastic manner. Whenusing a separate connection shaft, it is also possible to drive theconnection shaft via the motor.

The elastic elements which bring about the rotation compensation can becoil springs or spiral springs, similar to the mainspring of a watch.The spiral spring can be accommodated in the drive gear and inparticular in a pocket-shaped extension in the drive gear. The rotatingparts can be coupled rigidly and inelastically with one another and thecompensation can be produced by placing a compression spring between thetension rod and the push element associated the pertinent end of thetension rod.

The length of the tension rod can vary in accordance with the geometryof the window.

In order to conduct the push elements in a bend-resistant manner, theuse of guide rails that contain an undercut guide groove isadvantageous. The undercut guide groove is composed of in cross-sectionof a groove chamber and a groove slit.

The following description of the figures is limited to an explanation ofthe aspects necessary to understand the invention. A number ofmodifications are clearly possible. As will be appreciated, one of skillin the art will understand the less important details that are notdescribed in the drawings.

The following drawings are not necessarily to scale. For instance, topromote a better understanding of the invention it may be that certainareas have been enlarged. Moreover, the drawings are schematic in natureand do not contain every detail which may be present.

Exemplary embodiments of the invention are shown in the drawings.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway perspective view of the rear passengercompartment of an exemplary motor vehicle equipped with a roll-up windowshade according to the present invention.

FIG. 2 is a partially cutaway front view of the roll-up window shade ofFIG. 1.

FIG. 3 is a schematic exploded perspective view of the connectionbetween one of the drive gears and the winding shaft of the windowroll-up shade of FIG. 1.

FIG. 4 is a partially cutaway front view of an alternative embodiment ofa roll-up window shade according to the present invention in which thedrive gears are arranged on the connection shaft without rotationalplay.

FIG. 5 is a partially cutaway front view of an alternative embodiment ofa roll-up window shade according to the present invention in which theconnection shaft runs coaxially through the winding shaft.

FIG. 6 is a partially cutaway plan view of an alternative embodiment ofa roll-up window shade according to the present invention in which thecompensation of the shade is accomplished with the aid of compressionsprings.

While the invention is susceptible of various modifications andalternative constructions, a certain illustrative embodiment thereof hasbeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific form disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, the rear passenger compartment of aan exemplary motor vehicle is shown. The right interior side is shown inFIG. 1. The right side is the mirror image of the left interior side.Unless otherwise indicated, the explanations for the right automobilebody side are also apply to the left automobile body side. The depictionin FIG. 1 is simplified; thus, for example, automobile body interiorstructures, such as the reinforcements, affixing elements are not shownsince they are not necessary for an understanding of the invention.

The illustrated automobile body section 1 has a roof 2. A C column 3leads downwards from a side of the roof to a car bottom assembly. Acorresponding C column can also be provided on the opposite side of themotor vehicles. In this case, the interior side of the C column 3 isprovided with a lining 4. A rear window 5 extends downward from the rearedge of the roof 2. The rear window 5 is bound on the upper side by awindow upper edge 6. The side edges 7 of the windows extend toward eachother. The side edge 7 shown in FIG. 1 extends into a corner area 8 intothe window upper edge 6.

The width of the rear window 5 is greater at the level of the beltlineof the automobile body than in the area of the window upper edge 6. A Bcolumn 9 is provided at a distance in front of the C column 3. A rearright-side door 11 is hinged to the B column in a known manner. Theright rear-side door 11 contains a window section 12, which is dividedup by a vertical brace 13 into a substantially rectangular section 14and an approximately triangular section 15. The interior of the vehiclefurther includes a back seat bench 15, with a back seat area 16 and aback seat back 17. The back seat area 17 lies on a floor assembly 18. Arear shelf 19 extends between the upper rear edge of the back seat back17 and the rear window 5.

In accordance with the invention, the rear window 5 is provided with arear window roll-up shade 21 of which only the shade 22 is shown inFIG. 1. Other window shades are provided for the side window 12.Specifically, a shade 23 is provided for the rectangular window section14 and a shade 24 is provided for the triangular section 15. The drivefor the shades 23 and 24 is the same as the drive for the rear windowshade 21. Accordingly, only the structure of the drive for the rearwindow shade will be described in detail herein.

As shown in FIG. 2, the rear window shade 21 includes two guide rails 25and 26 and a drive system 27. The guide rails 25 and 26 are arranged ina mirror image to one another and follow the side edge of the rearwindow 5. Unlike as shown in FIG. 2, the guide rails 25 and 26 convergeas they extend in the direction of the roof 2.

Since the two guide rails 25 and 26 are identical, a description of theinterior structure of the guide rail 26 is sufficient for anunderstanding of the invention. Such description is also applies for theguide rail 25. In the guide rail 26, an undercut guide groove 27 isprovided. The profile of the undercut guide groove 27 is composed of agroove chamber 28 and a groove slit 29. The width of the slit 29 issmaller than the inside width of the groove chamber 28, wherein theundercut structure is produced.

The two guide rails 25 and 26 conduct a tension rod 31 on which one edgeof the shade 22 is affixed. The tension rod 31 includes a middle piecein which two end pieces 32 and 33 are supported in a telescoping manner.The middle piece can sit in a hose-like loop formed on the shade 22.Each of the end pieces 32 and 33 has a telescoping rod 34 with a slidepiece 35 sitting on its free end. The telescoping rod 34 hascross-sectional dimensions in that enable it to be conducted through theslit 29 with clearance. The cross-sectional configuration of the slidepiece 35 is adapted to the cross-sectional configuration of the groovechamber 28, which can be, for example, circular. The end of the shade 22opposite the tension rod 31 is affixed to a winding shaft 36.

The drive device 27 is used to move the shade 22 between an extendedposition in which it is extended over the rear window 5 and a retractedposition in which the tension rod 31 either lies on the rear shelf 19 oris retracted into the slit provided in the rear shelf. The drive device25 includes two identical linear flexible push elements 38 and 39. Eachof the push elements 38, 39 includes a core 41 having a circular crosssection and a coil 42 that is affixed on the outside of the circularcore 41. This produces a kind of elastically flexible toothed rack withteeth all around. The outside diameter of the push elements 38, 39corresponds to the inside width of the groove chamber 28. In this way,the two push elements 38, 39 are conducted in their corresponding guiderails 25 and 26 in a buckle-free manner and can transfer compressionforces. The diameter of the push elements is larger than the slit width29 so that they cannot be buckled laterally through the slit 29 evenwith compression stress.

The drive device 27 further includes a geared motor 43 whose outletshaft 44 is rigidly connected to the axle pins 45 of the winding shaft36. A spur gear 47 or 48 sits on the two shaft journals 45 and 46. Thespur gear is provided with a gear-tooth system on its circumferentialsurface that permits a positive-locking meshing with the correspondingpush element 38, 39. The two push elements 38, 39 are pressed in aradial direction against the corresponding drive gear 47, 48, so thatthe engagement is consistently maintained. The push elements 38, 39 lieon the same side relative to the axis of rotation of the correspondingdrive gear 47, 48 on which the shade 22 is extended from the windingshaft 36.

The gear 47 is rotatably supported on the shaft journal 45 and the gear48 is rotatably supported on the shaft journal 46. The operative driveconnection, via which a driving torque is transferred, is shown in FIG.3. The details shown in FIG. 3 apply for both drive gears 47 and 48.

The drive gear 47 has a disk-like shape with a cylindricalcircumferential surface area 50 in which grooves 51 comprise the geartooth system. The grooves 51 run at an incline and take up the pertinentsection of the coil 42. The gear 47 includes an extension 52 coaxial tothe outside circumferential area 50. A bearing borehole 53 is containedconcentrically in the extension 52 that enables the gear 47 to berotatably supported on the shaft journal 45. In this case, theextensions 52 each comprise a spring housing for a spiral spring 54 thatproduces a rotationally elastic connection between the shaft journal 45and the gear 57. In this respect, the shaft journal 45 includes aturned-up lip 46 at the corresponding location, which is used as anabutment for an opening 47 provided on the inner spring end. The outsidespring end also has an opening 48, which can be connected, in apositive-locking manner, with a lip 49. The lip 49 points radiallyinwardly from the outside circumferential area of the extension 52.

As can be understood from the operational description below, a relativerotation with respect to the winding shaft 36 is achieved via acorresponding dimensioning of the effective diameter of the gear 47relative to the roll body that is formed on the winding shaft 36 by thewound shade 22. The dimension of this relative rotation is approximatelyand at most one rotation. In this way, a spiral spring 54 which has arelatively short effective path can be used.

The figures are not to scale and are intended to illustrate theimportant features of the drive concept according to the invention. Thepertinent dimensions of the guide rails 25 and 26 and the outsidediameter of the two elastic, pliable push elements 38, 39 can be readilydetermined from actual practice.

An elastically flexible storage tube 61 or 62 is arranged on theopposite side of the pertinent gear 47, 48 from the individual guiderails 25, 26. To a large extent, the storage tubes 61, 62 can be placedfreely in the motor vehicle in accordance with the spatial conditions. Adescription of the measures which are taken in order to keep the storagetubes 61 and 62 stationary is not necessary for the understanding of theinvention. Additionally, a housing may be provided to surround the gear47 or 48. The housing can contain a corresponding tangential boreholefor the passage of the pertinent flexibly-elastic push element 38, 39.

The operation of the illustrated embodiment is as follows. It is assumedthat initially the shade 22 is completely (i.e., as much as possible)wound on the winding shaft 36. When wound, the spiral springs 54contained in the two gears 47, 48 are slightly biased. As a result ofthe bias, the push elements 38 and 39, meshed and thus coupled in apositive-locking manner are elastically biased in the direction of thetwo slide pieces 35 of the tension rod 31 and fit snugly there. The biasforce of the spiral springs 54 holds the shade 22 between the windingshaft 36 and the tension rod 31 so that it is taut.

Beginning from this position, if a user wishes to extend the rear windowroll-up shade 21, he starts the geared motor 43 with an electric switch.The running geared motor 43 turns the winding shaft 36, together withthe two shaft journals 45 and 46, which are coupled without rotationalplay, in the unwinding direction of the shade 22. The two drive gears 47and 48 move in the same direction of rotation. Since their effectivediameter coincides with the outside diameter of the roll body on thewinding shaft 36 when the shade 22 is completely wound (i.e., with thewindow shade opened), the two push elements 38 and 39 first move atexactly the same speed as the tension rod 31 at the movable front edgeof the shade 22.

As the shade 22 is increasingly unwound, the roll body on the windingshaft decreases in size. Consequently, less shade is released perrotation of the winding shaft 36 than the two elastically flexible butshear-resistant push elements 38, 39 would traverse with a rigidcoupling and at the same angular rotation. As a result of the rigidcoupling with the shade 22, the push elements 38, 39 are forced to moveat the same speed as the shade 22, which as a result leads to theslowing down of the rotational movement of the two drive gears 47 and 48as compared to the rotational movement of the winding shaft 36. In thisway, the spiral spring 54 is substantially wound up in a manner similarto the mainspring of a watch. However, depending on the dimensions andthe length of the shade has extended, the extent of the relativerotation is limited to approximately one rotation between the windingshaft 36 and the drive gear 47 or 48. At the end of the extensionmovement, when the tension rod 21 has arrived at the upper edge of thewindow, the cloth tension in the shade 22 will thus be somewhat greaterthan at the beginning.

The retraction of the shade is carried out analogously in the reversedirection, wherein the two spiral springs 54 once again relax by thecorresponding extent. At the end of the retraction movement, the tensionrod 31 is again on the rear shelf 19 and the remaining residual tensionin the two spiral springs 54 provides the required cloth tension in theshade 22. Since the spiral springs 54 have identical dimensions, thesame forces also act on the tension rod 31 on both ends.

As a result of the illustrated arrangement, the two shaft journals 45and 46 that are coupled rigidly to the geared motor 43 move at the samerotational speed and thus produce the same drive effect for the twodrive gears 47 and 48. Furthermore, the push elements 38 and 39 now movein an essentially stretched state. Since the drive effect is introducedright at the foot end of the two guide rails 25 and 26, complexdeflections are not required to bring the two push elements 38, 39 toone common drive source. Each push element 38, 39 has its own drivesource, which is arranged in such a manner that a minimal deflection ofthe push element 38, 39 from the completely stretched, straightcondition is required. In this way, the friction is enormously reduced,compared with the arrangements found in the prior art. Also the storagetubes 61 and 62 move primarily in a straight line, and since they areflexible, they can be placed in the motor vehicle in any manner.

The force which must be produced by the motor 43 corresponds to theforce which is required to further wind up the two spiral springs 54with the rotational travel, in comparison with the winding shaft 36, aswell as the very small friction to which the two push elements 38, 39are subjected. This friction is very small since the two guide rails 25,26 move primarily in a straight line. The radius of curvature is alsoextremely large at the most narrow location.

The illustrated embodiment is a fundamental arrangement. The illustratedmotor 43 is a geared motor that acts on the outside end of the shaftjournal 45 so that the drive gear 47 is located between the windingshaft 36 and the geared motor 43. Those skilled in the art will readilyappreciate that the drive can also be introduced at the shaft journal 45between the drive gear 39 and the winding shaft 36.

In the embodiment of FIG. 2, each drive gear 47, 48 is coupled by itselfin a rotationally elastic manner. An embodiment in which the two drivegears 47 and 48 are seated on a connection shaft 65 is shown in FIG. 4.The connection shaft 65 moves like a bearing axle through thetube-shaped winding shaft 36 as shown in the cut away portion of FIG. 4.The other end of the connection shaft 65 is in turn coupled withoutrotational play to the outlet shaft 44 of the geared motor 43.

The diameter of the connection shaft 65 is clearly smaller than theinside width of the tube-shaped winding shaft 36. An annular space 66 isproduced in which a coil spring 67 is located. The coil spring isanchored at one end in a bearing ring 68 that is coupled to theconnection shaft 65 without rotational play via a pin 69. The pertinentend of the winding shaft 36 is supported on the bearing ring 68. Theother end of the coil spring 67 is connected without rotational play toa ring piece 71, which in turn is also connected without rotational playto the winding shaft 36 with the aid, for example, of reinforcing seams72. The other end of the winding shaft 36 is supported, with littleclearance, on the connection shaft 65. Otherwise, the structure of thisrear window roll-up shade 21 is not different from the rear windowroll-up shade 21 of FIGS. 2 and 3.

The relative rotation between the winding shaft 36 and the drive gears47 and 48 required during operation is brought about here via a coilspring 67, which produces the rotationally elastic connection betweenthe connection shaft 65 and the winding shaft 36. Otherwise, theoperation is also the same as the embodiment of FIGS. 2 and 3.

An arrangement in which the connection shaft 65 does not pass coaxiallythrough the tube-shaped winding shaft 36, as in the embodiment of FIG.4, but rather is located parallel to and next to it is shown in FIG. 5.The two gears 47 and 48 sit on the connection shaft 65—again in such away that they, as with all the illustrated embodiment, are largelyaligned with an extension of the guide rails 25, 26, so as to produce aminimal deflection of the push elements 38, 39 and thereby the frictionforces remain small. A gear 75, which meshes with a front gear 76located on the shaft journal 65, is seated on the connection shaft 65.

In the embodiment of FIG. 5, there are several possibilities ofcompensating for the rotation between the drive gears 47 and 48 and thewinding shaft 36. First, the two gears 47 and 48 could be coupled withthe connection shaft 65, in a rotationally elastic manner, as with theembodiment of FIGS. 2 and 3. In that embodiment, the drive gears 47 and48 are rotationally elastically connected to the bearing journals 45 and46, which in turn are coupled to the winding shaft 36 without rotationalplay. Another possibility for attaining the required rotationcompensation is by coupling the front gear 76 in a rotationally elasticmanner to the shaft journal 65, as in the embodiment of FIG. 3.

Instead of accommodating the rotationally elastic coupling in the frontgear 76, the rotationally elastic coupling can also be carried outbetween the gear 75 and the connection shaft 65. In each case, theoperation is described as above. The advantages explained in thisconnection are also attained.

An alternative embodiment as to how the travel path difference betweenthe front edges of the shade 22 and the push elements 38, 39 can becontrolled is shown in FIG. 6. The basic structure of the shade 21,according to FIG. 6, corresponds to the structure shown in FIG. 2.However, the two drive gears 47 and 48 are seated on the shaft journals45 and 46 without rotational play, so that in this case a relativerotation between the winding shaft 36 and the two drive gears 47 and 48is possible. The travel path difference is controlled with the aid ofcompression springs 79. The cutaway part of the guide rail 26 in Fig.shows how the coil compression spring 79 is inserted between the freeend of the push element 39 and the slide piece 35. The dimensions areselected such that the compression spring 79, which is supported on thefree end of the push element 39, constantly exerts a pre-push force onthe tension rod 31. The compression spring 79 exhibits the largestlength when the shade 22 is wound on the winding shaft 36. When thewinding shaft 36 together with the two gears 47 and 48 are rotated bythe geared motor 43, the tension rod 31 begins to slow increasinglydown, as compared with the free ends of the two push elements 38, 39. Inthis way, the compression springs 79 contained in the two guide rails 25and 26 are increasingly compressed. Since the two drive gears 47 and 48are located directly below the lower end of the two guide rails 25 and26, connection tubes for a common drive gear are avoided, andcorrespondingly, the friction loss is reduced.

Those skilled in the art will appreciate that the drive concept forshades explained above in connection with FIGS. 2-6, is not limited touse with rear window roll-up shades. This drive concept can also be usedin connection with other type of shades, for example, side roll-upwindow shades for the rectangular window section 14 of the rear sidedoor or with a sunroof roll-up window shade.

Two drive gears are provided as an extension of the guide rails fordriving a roll-up window shade for a motor vehicle. The drive gears arecoupled to the winding shaft in a rotationally elastic manner. Thedriving is carried out via a geared motor, which acts either on thegears or on the winding shaft. The positioning of the drive gears as anextension of the guide rails avoids the guide tubes used in prior artarrangements. Thus, the friction losses found in the prior art, whichconsume up to 80% of the drive force, are avoided. Furthermore,manufacturing is simplified because the connection tubes having acomplicated shape are not needed.

1. A roll-up window shade for motor vehicles comprising: a rotatablysupported winding shaft; a shade having a first edge affixed to thewinding shaft; a tension rod connected to a second edge of the shadespaced away from the winding shaft; two guide rails each extending on arespective side of the shade when the shade is an extended position, thetwo guide rails guide the tension rod in a positive-locking manner; twopush elements each being conducted in a respective one of the guiderails, each push element carrying a gear-tooth system that acts on thetension rod; two drive gears arranged at first and second ends of thewinding shaft, each drive gear being allocated to a respective one ofthe push elements, wherein the push elements are operatively arrangedbetween the drive wheels and the tension rod; an electric drive motor;and a spring compensating element for compensating for differences inthe length of the shade as it is extended as compared to thecorresponding length of travel of the push elements in the guide rails.2. The roll-up window shade according to claim 1, wherein the tensionrod is configured so that its length is selectively variable.
 3. Theroll-up window shade according to claim 1, wherein a first end of theeach of the guide rails is arranged in the vicinity of the windingshaft.
 4. The roll-up window shade according to claim 1, wherein theguide rails extend parallel to one another.
 5. The roll-up window shadeaccording to claim 1, wherein each guide rail contains a guide groove.6. The roll-up window shade according to claim 5, wherein the guidegroove has a cross sectional configuration including a groove chamberand a groove slit, a diameter of the groove chamber being larger than aninside width of the slit so as to define an undercut guide groove. 7.The roll-up window shade according to claim 6, wherein each push elementis conducted in a buckle-resistant manner in the respective groovechamber.
 8. The roll-up window shade according to claim 1, wherein thegear tooth system of each push element extends around the push element.9. The roll-up window shade according to claim 1, wherein each drivegear is a front gear.
 10. The roll-up window shade according to claim 1,wherein each of the drive gears is connected to the winding shaft. 11.The roll-up window shade according to claim 1, wherein each of the drivegears is arranged coaxial relative to a rotational axis of the windingshaft.
 12. The roll-up window shade according to claim 1, wherein thetwo drive gears are seated on a connection shaft which is conductedthrough the winding shaft.
 13. The roll-up window shade according toclaim 1, wherein the two drive gears are seated on a connection shaftwhich runs parallel to the winding shaft.
 14. The roll-up window shadeaccording to claim 1, wherein the electric drive motor is coupled to thewinding shaft.
 15. The roll-up window shade according to claim 12,wherein the electric drive motor is coupled to the connection shaft. 16.The roll-up window shade according to claim 13, wherein the electricdrive motor is coupled to the connection shaft.
 17. The roll-up windowshade according to claim 12, wherein the spring compensating element islocated between the connection shaft and the winding shaft and the drivegears are connected to the connection shaft without rotational play. 18.The roll-up window shade according to claim 13, wherein the springcompensating element is located between the connection shaft and thewinding shaft and the drive gears are connected to the connection shaftwithout rotational play.
 19. The roll-up window shade according to claim13, wherein a gear pair is provided with one of the gear pair beingcoupled to the winding shaft and the other of the gear pair beingcoupled to the connection shaft.
 20. The roll-up window shade accordingto claim 1, wherein the spring compensating element comprises a coilspring.
 21. The roll-up window shade according to claim 1, wherein thespring compensating element comprises a spiral spring.
 22. The roll-upwindow shade according to claim 21, wherein the spiral spring is seatedin a recess of one of the drive gears.
 23. The roll-up window shadeaccording to claim 13, wherein the spring compensating element comprisestwo springs, one of the two springs being located between one of thedrive gears and the connection shaft.
 24. The roll-up window shadeaccording to claim 1, wherein the spring compensating element comprisestwo springs, one of the two springs being located between the windingshaft and a corresponding one of the drive gears.
 25. The roll-up windowshade according to claim 1, wherein the spring compensating elementcomprises two springs, one of the two springs being located between thetension rod and one of the push elements and the other of the twosprings being located between the tension rod and the other pushelement.
 26. The roll-up window shade according to claim 25, wherein thesprings are compression springs.
 27. The roll-up window shade accordingto claim 1, wherein each push element has an associated engagementmechanism for keeping the respective push element engaged with itsassociated drive gear.
 28. The roll-up window shade according to claim1, where a separate gear housing is provided for each drive gear. 29.The roll-up window shade according to claim 1, wherein each push elementhas a corresponding storage tube for receiving an empty rail of the pushelement when the shade is in a retracted position.
 30. The roll-upwindow shade according to claim 29, wherein each storage tube is made ofa flexible material.